Device for erosion control

ABSTRACT

An elongated tubular assembly comprising a plurality of tubular units disposed in end-to-end relationship, each unit comprising a lower section (1) composed of a variably rigid impermeable contact base (3), and an upper section (2) with a variably rigid protruding hull (5) designed to deviate surrounding fluid flows, the lower (1) and upper (2) parts being connected to each other at least along their longitudinal edges encompassing to such extent an internal space in which a ballast (15) can be admitted through registered hull openings (7), such flexible base and hull combination being designed to give stability to a light-weight version of said unit even in an environnment of heavy fluids, somewhat in the manner of a flat fish, for works including but not limited to ground erosion control and flood control.

The invention described herein concerns a protruding hollowfoundationless springy elongated modular device for the control of soilerosion and soil migration in a fluid environment. An economy of weightis achieved through the combination of a flatfish type variably rigidcontact base and a streamlined hull. The invention also relates to theplacing of units in end-to-end and/or perpendicular relationship toserve not only for the above purpose but also for other purposes such asflood, mud, aquaculture or other dams, and for the protection ofvulnerable objects such as cables and utility lines in an active fluidenvironment.

The major purpose of the erosion-control device is the fixation ofsubmersed sedimentary counterforts and dunes either by controlling thespeed of the erosion fluid or by opposing a stationary implant to themigration of natural sedimentary ripples, thus provoking their increasein size and their fixation.

Surrounding fluids (air and water) cause soil erosion, in a generalmanner, in maritime and land environments, because of the speed oferosion which can be reached either by nature or following humanintervention.

A device slowing down a maritime- or river-current can be compared withthe artificial reproduction of a sedimentation ripple (mega-ripple)which forces the current upwards from the soil and thus favors thesettling and concentration of the shifted mobile elements into new,natural sedimentation ripples simulating the profile of a delta orestuary thereby regenerating mobile shores.

Traditionally such a sedimentary action has been sought as a marginalfunction of oversized heavy shore constructions. Even when notoversized, the energy-reducing devices are made, more often than not, byfilling envelopes of supple fabric used in earth works (bags, rollers,etc.) with such heavy ballast as sand or concrete which ensuresstability and their unfolding on their own. When weighted in such amanner, the devices assume the shape of an extended semi-cylindricalwing and tend gradually to submerge in the sand under their own weight.Other technologies are employed to prevent this gradual submergingwhich, as in U.S. Pat. No. 4,690,585, (Holmberg) consist in laying theerosion control system on a porous apron of fabric used in earth works,anchored to the soil with peripheral pockets (drawing 1a).

Should these convex, relatively rigid, erosion slowing-down devices befixed to a flexible and porous apron, the hydrostatic overpressureexerted on the wing is carried almost entirely through the apron to thesoil below the structure which can cause it to lift and capsize. Inaddition, such devices can be laid only when loaded: they are heavy,susceptible to damage, occupy much space, are unpleasant in appearanceand immovable. When made in long sections, they are prone tolongitudinal fragility and can be broken by changes occuring in thesoil.

One of the characteristics of the present invention lies in thepossibility of assembling movable light-weight low-profile sedimentationstructures in water. It may also prove imperative to change the locationand/or orientation of these devices to obtain a better reproductioneffect, taking into account the features of the maritime factorsoccuring within the operational zone.

On emerged land, light-weight supple devices, adapted to the aerialfluid constraints, are used to fix dunes behind protective wind breakersby the use of fabric netting spread on the ground (drawing 1c) or setvertically (drawing 1).

One of the purposes of the invention described herein is to fixsubmarine dunes using a light easy-to-install device adapted to themaritime fluid and to remedy the heavy or massive structures' faults orat least to limit them satisfactorily, while allowing better control ofsoil erosion using a simple and multi-functional device (maritime, riveror land).

This purpose is met in the invention by laying the device, the lowersection of which has elements to fix the device to the soil while theupper section has parts reducing the energy of erosion fluids--theseparts comprising a variably rigid hull, while the fixing elementscomprise a variably rigid non-permeable base the underside of which issubjected to a first hydrostatic pressure lower than the hydrostaticpressure acting upon the upper side of the above-mentioned fixingelements and resulting from the pressing force of the erosion fluidsacting upon the hull. In addition, the top and bottom parts are rigidlyconnected at least on the edges, thereby forming an internal space whichmay be, at least partly, filled with ballast or with the elasticmaterial of which the fixing elements and/or the energy-reducingelements may be made, it being posible that this elastic material make asolid piece with the above-mentioned elements.

In a first embodiment, the upper and lower parts are connected in aseparable way.

In a second embodiment, the device is hollow and made up of a singlepiece.

In yet another embodiment, the device is solid and made up of a singleelastic piece.

A merit worth highlighting is that the ends and edges of the hull havemodular connecting elements allowing connection with similar devices ofthe same type to form a continuous unit. These elements comprise a maleprofile dovetailing with a female profile to create a longitudinalsection and/or comprise a profile with side-adjusting walls, adjustingat least in part and in a continuous manner to the upper part's sidewalls to form lateral sections.

Due to its impermeable base preventing submergence in the soil, such adevice laid in a direction which crosses the direction of the erosivefluids is subjected to hydrostatic pressure which cannot be transmittedto the soil due to the impermeability of its base. That is why thesystem creates a pressure differential between the two surfaces of thebase and is forced to the soil by a force which increases as the energyof the erosive agents increases.

Should this device be used on a sea coast, the effect of this slowingdown is sedimentation. The modular device, laid in rows at right anglesto the erosive current, slows down the current and causes the sedimentto settle.

Should converging rows be laid towards a narrowing gullet, the modulardevice will accelerate the current, dissipate the sediment and henceresult in controlled erosion.

Although the domain of the present invention extends naturally to thecontrol of land erosion as well as marine erosion by slowing downerosion fluids, it will be better understood if illustrated by existingexamples of its applications to marine or river erosion control.

The invention is illustrated by the following description with encloseddrawings:

drawings 1a to 1c present perspective views of conventional massivedevices to slow down erosion;

drawings 2a and 2b present perspective views of the device described inthis patent at various sites;

drawings 3a to 3c present perspective views of the various manners inwhich the device of this invention can be made;

drawings 4a to 4c present perspective views with partial cross-sectionsof various embodiements of this invention;

drawing 5 presents a perspective view of one particular embodiement ofthis invention;

drawing 6 presents a perspective view of the device described in thisinvention together with the anchoring elements;

drawing 7 presents a perspective view of an assembly of several devicesaccording to the invention.

Drawings 1a to 1c illustrate the previous state of the art.

As shown in drawing 2a, the device (R) which is the subject of thisinvention to slow down erosion (current C, wind V) is connected inmodules with other devices of the same type to obtain an assembly(R1,R2, . . . Rn) set in relation to the shore in one or more contiguousrows, partly submerged and causing the increase of maritime and eoliansediment action. Generally, the device (R) comprises a lower section (1)with anchoring elements and an upper section (2) with elements reducingthe energy of erosive fluids. The energy-reducing elements comprise aprotruding variably rigid hull (5).

As shown in drawing 2b, the device slowing down erosion which is thesubject of this invention contains at least one module (R) comprising animpermeable base and a hull. It can be placed equally well on submergedor emerged land and optimum accretion effect is obtained when module (R)is at right angles to the direction of the erosive fluid prevailing inthe given environment (current, tides, rain, water drainage, wind,etc.).

Drawing 3a shows the device manufactured in two parts, the upper section(2) being equipped with means to reduce the impact of erosive factorsand manufactured as a rigid protruding hull (5) of parabolic profilewith a convex summit and horizontal lateral edges. The upper section (2)is connected to the lower section (1) by a fixing arrangement(preferably dismountable) for instance bolts (6).

The lower section (1) contains means to fix it to the soil, made of animpermeable base facing the soil. The impermeable base (3) containsdihedral surfaces (3a) whose peak angle is greater than 100° forinstance and whose lateral extension inside the hull (5) forms ahorizontal strip (3b) and whose longitudinal extension forms aperipheral skirt (3c) outside the hull (5), which mitigates erosionrelated to disturbances at the ends of the hull and can be used to linkup with another module or to a soil anchor, thanks to the slots in whichappropriate fixing items could be placed (belts, etc.). The ends of thedevice create an opening between base (3) and hull (5).

Drawing 3b shows a device comprising a flat impermeable base (3) and aclosed hull (5) whose lateral walls form a dihedral plane inclined oneach side of the peak edge prolonged by flattened lateral edges. Theends (5a, 5b) are respectively made as male and female parts, to allowthe linking of the individual modules. The angle of the dihedral planeis selected at around 90°, for example, to enforce the erosive agent'sascending motion which causes it to slow down. Openings (7) can be madein the hull equipped with plugs (8) to introduce ballast which may be anabsorbant sponge such as is used for liquid storage.

Drawing 3c shows a module of the invention device which has a parabolichull and flattened lateral edges. Openings (7) are made in the hull (5)to permit filling with ballast, it being possible to equip them withplugs or one-way valves (8) to close them from the inside. Theimpermeable base (3) is fitted with a peripheral skirt (12) at least onits longitudinal edges, this being dug into the soil to a depthsufficient to hinder the lateral dissemination of the pressure of theerosive fluids under the device. The ends (10 and 11) are maderespectively with a convex male and concave female profile, so that twomodules of the same kind can be connected in a manner at least partlyarticulated to form a continuous longitudinal unit.

Among others, a prototype of the following overall dimensions wasmanufactured:

    ______________________________________                                        length                 60    cm                                               width                  9     cm                                               rigid, convex, impermeable base                                                                      5     mm                                               height with parabolic profil                                                                         6     cm above                                         soil                                                                          ______________________________________                                    

Upper section set on lower section, but not fastened.

Mean current speed in the sand-carrying environment (river) 7.5 km/hr.

A total sand accretion (covering the entire device) has been obtainedwithin 1 hour.

On drawing 4a the wall of base (3), of roughly parabolic shape, may bethicker in its middle than on the edges to gain variable longitudinalrigidity and more rapid flexing deformation on the edges which causesgreater contact of the device with the light, running soil under thebase surface. Openings (7) allow circulation of the erosive fluid andsedimentation within the space inside the device.

Drawing 4b shows a device in which the internal space between the lowersection (1) and upper section (2) is partly filled with granular ballast(15), with openings (7) made near the peak of the hull (5), therebyallowing a gradual improvement in the device's stability.

Drawing 4c shows a single-piece device which may be hollow or solid andcomprises upper section (2) and lower section (1).

In this case the interior is filled with the same elastic material asmakes up the fixing and energy-reducing elements which are the base (3)and hull (5) respectively.

Once a device has been laid, the underside of the impermeable base (3)is subjected to a hydrostatic pressure lower than the hydrostaticpressure caused by the erosive fluids acting on the upper side of thebase (3) and/or the hull (5). The slight oscillations of the variablyrigid impermeable base suck the underlying sand into contact with theconcave underside of the underlying base and/or with the groovedunderlying base.

Drawing 5 illustrates an advantageous embodiement comprising, inparticular, the impermeable base (3) and hull (5) with lengthwise slot(5a) permitting the rapid entry of the ballast, or of erosive fluids andnatural sediment, or of a classical energy-reducing unit of earth-worksfabric material or of a pipe-line.

Drawing 6 shows how a device can be made with blind seats (18) in theside wall of the hull (5) lower section and encroaching on theperipheral edges. These seats (18) are to hold the anchoring elements(9) which are fitted and adapted to protrude beyond the peripheral edgeand to dig into the soil. They may also serve for handling the module.

Drawing 7 in conjunction with drawing 3c shows how modular devicesdescribed in the invention can be linked in two directions. The femaleend (11) possesses side-walls (14) formed by the extensions of hull (5),which adjust perpendicularly to the side walls of hull (5) of a moduleof the same type, to form a more or less continuous lateral chain. Themale end (10) of convex and/or protruding profile dovetails with thefemale end (11) of concave or recessed profile.

Generally speaking, and with respect to all the drawings, it must bestressed that the device, once it is set on the soil or dug into thesoil, cannot be moved vertically or laterally by the action of theerosive fluids nor can it float due to lower section (1) which isequipped with elements to fix it to the soil comprising the base (3),assisted if required by anchoring elements (6) or some ballast (15),depending on the extracting forces. The device is additionally securedin place by all weighing-down agents or anchors depending on therespective densities of the device and the erosive fluid as well as theenergy of this fluid in the operation zone which may be reduced to theirminimum by the lack of archimedes force under the device.

A first hydrostatic pressure acts on the underside of base (3) lowerthan the hydrostatic pressure of the erosive fluid due to theimpermeability of the base surface which may for instance be laterallysupplemented with a waterproof skirt (12) sunk into the soil.

When the erosive fluid (for example rain, sea current, tides or wind)increases its erosive speed, the impermeability of the base hinders thispressing force from being transmitted to the soil below the device andthe variably rigid base and hull enhance the hydrostatic pressuredifferential by their suction cup effect as compared to that exerted onand/or inside the hull by erosion fluids.

The surfaces represented by base (3) and hull (5) thus act as a suctioncup which forces the device against the soil and the soil under thedevice.

Base (3) hull and skirt (12) are best made of impermeable elastomer andthe adherence to the soil can be increased by etching the underside ofthe base similarly to a tire pattern.

The device can be made a single-piece unit by rotational molding ofpolyethylene. Cement or ferrocement are also satisfactory materials whencoating a springy structure.

The device according to the invention is made to withstand theextracting force of the erosive fluids which can reach 12 tons persquare meter on the shores and 100 kilograms per square meter in thecase of eolian erosion.

The device can also be used to direct the wind away from a dune beingeroded or to slow down the flow of water in open-cast mines causing,respectively, an increase in the dune's height and the lifting andreinforcement of the earth.

One advantageous embodiement of the concave underside of the base allowsthe large concave variably rigid arch to flex and adhere to the groundand opposes slipping or tearing forces. In the early installation phase,anchoring appliances and ballast inherent to the invention allow a firmgrasp of the device in the soil.

In an advantageous embodiment, the peripheral edges of hull (5) are at atangent to the horizontal, or with a convex drape, thus allowing thedug-in device to better oppose extraction by the erosive fluids.

In another manner of embodiement, base (3) is made of a strong,impermeable cloth which is flat when at rest and will become concavewhen at work.

In order to impart an ascending motion to the erosive fluids, the hull(5) should protrude for instance with a parabolic, semi-cylindrical ordihedral shape and possess horizontal peripheral edges or edges dug intothe soil.

When advantageously implemented, the relation of width to height shouldpreferably be greater than 1.5 so that the base surface could have awidth of 3 times its height for instance and length between 1.5 and 6times its width for example.

The openings (7) can have a cross-section of from several squarecentimeters to several square decimeters, of uniform, preferably ovalshape to allow them to be covered over from the inside. Due to its lowweight, the device can be used on channel slopes and can be suspended onany kind of anchoring appliance fixed to sockets (18) or in slots (21).

In cases where the upper section and the lower section do not constitutea single piece, they are to be linked by bolts or any other meansreconcilable with the chemical and mechanical properties of thematerial.

We claim:
 1. An elongated tubular assembly for the control of soilerosion or soil migration in a fluid environment, said elongated tubularassembly comprising; a plurality of tubular units disposed in end-to-endrelationship, each unit having a lower section (1) and an upper section(2), said lower section (1) having longitudinal edges and composed of avariably rigid impermeable contact base (3), said upper section (2)having longitudinal edges and a variably rigid protruding hull (5)designed to deviate surrounding fluid flows, the lower section (1) andthe upper section (2) being connected to each other at least along theirlongitudinal edges defining an internal space therebetween in which aballast (15) can be admitted through registered hull openings (7) insaid upper section, said variably rigid base and hull combination beingdesigned to give stability to said unit even in an environment of heavyfluid flow to control soil erosion or soil migration.
 2. An elongatedtubular assembly according to claim 1, being made of a single solidvariably rigid piece of material.
 3. An elongated tubular assemblyaccording to claim 1 characterized by the upper part (3) being connectedin disassemblable manner with the lower part (2).
 4. An elongatedtubular assembly according to claim 1 characterized by the sides, endsand edges having dovetailing male and female shaped elements(1,5,10,11,14) and seats (18) and slots (21) allowing the anchoring,welding, fastening, transport, stacking and installation of a pluralityof tubular units in longitudinal and lateral assemblies in one or morelayers.
 5. An elongated tubular assembly according to claim 1 whichincludes registering units to define a barrier, said registered hullopenings (7) being on the side where a surrounding fluid must becontained.
 6. An elongated tubular assembly according to claim 1, thevariable rigidity of which is obtained by the base (3) having agenerally concave underside.
 7. An elongated tubular assembly accordingto claim 1, the variable rigidity of which is achieved by the base (3)wall having variations of thickness along its width.
 8. An elongatedtubular assembly according to claim 1 characterized by being hollow, andhaving a longitudinal slot along the hull (5).
 9. An elongated tubularassembly according to claim 1 the lower section (2) and upper section(3) are made of a single piece with an enclosed structure.